1. Field of the Invention
The present invention relates to an information recording and reproducing device and method, more particularly, for recording digital information in sector units on data storage media such as optical disks.
2. Description of the Related Art
In an information recording and reproducing devices for recording and reproducing digital information, magnetic disks, optical disks or the like are used as recording media. In such devices, the recording area of the disk is divided up into minute segments called sectors, and recording and reproducing are effected by the sector. The size of the sector is usually from 512 bytes to 2 Kbytes.
Such a recording and reproducing device, in order to achieve random access, must identify each individual sector without mistake. For this purpose, a track sector address is written at the head of each sector as an identifier. This is usually called ID. The ID plays a vital role in recording or fetching of information. Therefore the recording of ID is usually duplicated a plurality of times so that the target sector can be accessed even if some of the information of ID is lost due to media defects etc. For example, in the case of a 128 MB magneto-optic disk, the same track sector address is written three times, while in the case of a DVD-RAM it is written four times.
Usually, there is provided a gap area (called "GAP area") immediately after an ID area in which IDs are recorded. The GAP area is a buffer area for the purpose of effecting transition to recording operation after ID reproduction. After the GAP area a data record area follows.
In particular, for a recorded and reproduced optical disk, test emission from a laser diode is performed from the GAP area for each recorded sector so as to calibrate the emission power for recording. For this reason, in the optical disk, this GAP area is also known as the ALPC (Automatic Laser Power Control) area. The laser power is increased up to recording power for this calibration, it must be performed in an unrecorded data area i.e. GAP area.
The GAP area from the end of the ID to the data recording area may be made as small as possible for recording more information.
Accordingly when information is recorded, the information recording and reproducing device must read the ID and then rapidly determine whether the sector in question is a sector that is to be recorded. Then, the device starts recording operation simultaneously with the beginning of data recording area coming immediately after the GAP area. In particular in an optical disk device, since, as mentioned above, calibration of the recording power of the semiconductor laser is performed in the GAP area for each recording sector, it is necessary to make a decision as to whether or not the sector in question is one that may be recorded earlier than the timing when the data record area starts.
The specific operation of a prior art information recording and reproducing device in when data is recorded will now be described.
FIG. 4 is a block diagram of the prior art information recording and reproducing device.
In FIG. 4, the information recording and reproducing device comprises an optical head 401, a head amplifier 402, an analogue read channel 403, a data demodulator 404, a address demodulator 405, first to fourth preset registers 406-409, first to fourth comparators 410-413, a write gate start pulse generator 414 and a write gate generator 416.
The optical head 401 records signals to an optical disk 400 and reproduces signals from the optical disk 400 by using a laser beam. The optical head 401 includes a laser diode and a photodetector.
The head amplifier 402 produces an RF signal by amplifying the signal from the photodetector.
The analogue read channel 403 equalizes and digitizes the RF signal read from the head amplifier 402.
The data demodulator 404 demodulates the data from the digitized output of the read channel 403. The address demodulator 405 demodulates track sector address from the digitized output of the read channel 403.
The preset registers 406-409 store the track and sector address of the sector set beforehand, which is to be recorded. In this example, it is assumed that the address is written four times, these having respective identifying bits, therefore four preset registers 406-409 are shown.
The first comparator 410 compares the address output from the address demodulator 405 with the address stored in the first preset register 406. If they are the same, the first comparator 410 outputs a detection pulse. The second to fourth comparators 411-413 likewise output a detection pulse if the address output from address demodulator 405 is the same as the address stored in the second to fourth preset registers 407-409.
The write gate start pulse generator 414 sends a pulse to the write gate generator 416 when a certain condition of the detection pulses from four comparators 410-413 is satisfied. The condition, for example, is satisfied when detection pulses are detected from two or more of four comparators 410-413, with the output timing of fourth comparator 413 (if there is no output from fourth comparator 413, the timing is interpolated).
Record gate generator 416 generates a write gate signal with length corresponding to the length of the data record area in a sector. The write gate signal is a signal to control the data recording operation. The recording operation is performed when the write gate signal is active (high), while the recording operation is not performed when the write gate signal is inactive (low). In the following description, a term "a write gate" is often used, which means a write gate signal. That is, the recording operation is performed when the write gate is open, while the recording operation is not performed when the write gate is closed.
The information recording and reproducing device further comprises a data modulator 417 and a laser power controller 418.
The data modulator 417 applies modulation in respect of the data to be recorded.
The laser power controller 418 controls the output power of the laser that is mounted in the optical head 401. In addition to the modulated data, the write gate signal is input to the laser power controller 418. While the write gate is closed, the laser power controller 418 controls the laser power to the minimum necessary power (called "the read power") required for data reading from the disk, such that the data on the disk is not unintentionally overwritten or erased.
FIG. 5 is an operational timing chart of the information recording and reproducing device in the prior art. In FIG. 5, the recording position on the disk represents diagrammatically a signal format actually impressed on the disk. ID1 is the first ID of the IDs that are written four times, ID2 is the second ID, ID3 is the third ID and ID4 is the fourth ID. The symbols "x" written below ID2 and ID4 in FIG. 5 indicate fault of reading ID2 and ID4 (i.e. the results of checking CRC code encoded in the ID2 and ID4 are "NG (No Good)"). The symbols "o" written below ID1 and ID3 indicate success of reading ID1 and ID3 (i.e. the results of checking CRC code encoded in the ID1 and ID3 are "OK (All Right)"). The output signals of four comparators 410-413 are also shown respectively in the timing chart.
In the timing chart, since ID1 and ID3 have been read successfully, pulses are only generated in output signals of the first comparator 410 and the third comparator 412.
In FIG. 5, the output of write gate start pulse generator 414 and the write gate signal are also shown. Since two of the four IDs are read successfully, the write gate start pulse generator 414 outputs a pulse at the timing of the end of ID4. Triggered by this pulse, the write gate generator 416 opens the write gate, i.e. makes the write gate signal active (high) for a certain time. When the write gate is opened, i.e. the write gate signal is active, the recording operation can be started. The laser power controller 418 is therefore actuated actual data recording operation after laser power calibration.
In practice a servo control circuit of the optical head 401 is necessary.
FIG. 6 is another operational timing chart of the information recording and reproducing device in a prior art. In this figure, the output signals of four comparators 410-413, the write gate start pulse generator 414 and the write gate generator 416 are also shown. In this example, reading of ID1, ID2 and ID3 have failed, while reading of ID4 has succeeded.
Because of the success of reading ID4, in the timing chart, a pulse is output only in the output signal of the third comparator 412. Since only one of the four IDs could be read, no pulse is output by the write gate start pulse generator 414. Therefore, the write gate generator 416 keeps the write gate signal inactive. The recording operation is therefore not begun.
As explained before, the information recording and reproducing device has a signal processing unit called a read channel (the analogue read channel 403). The read channel 403 receives output from the head amplifier 402, equalizes received signal, digitizes equalized signal etc. and then passes the processed signal to the digital modulation and demodulation unit.